The ad charges that Obama is waging a "war on coal," and ties Grimes to the president, who is deeply unpopular in Kentucky — as he is nationwide.

"Across Kentucky, thousands of coal jobs are disappearing. Obama's war on coal is hurting whole families and communities. But Obama says he needs more allies in Congress to finish forcing his liberal agenda on our country. That's why here in Kentucky Obama's supporting Alison Grimes," a narrator says in the ad.

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The PAC is spending $90,000 to air the ad starting Wednesday through Dec. 17.

Both sides have been lobbing coal-focused attacks back and forth, as the coal industry makes up a significant part of Kentucky's economy.

Grimes has questioned McConnell's commitment to defending coal, while Republicans tie her to Obama and Sen. Harry Reid (D-Nev.), who once said "coal makes us sick," at every opportunity.